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111Wh <br /> D. Duplicates and Spikes <br /> + Every tenth sample is analyzed in duplicate. The duplicate <br /> aliquots arc carricd through the entire workup and analy- <br /> tical scheme. Cure is taken to assure that soils and <br /> hazardous wastes are duplicated at least as frequently as <br /> waters and wastewaters. How closely . the results compare <br /> with each other provides a measure of precision for the <br /> } <br /> determination. <br /> The same sample which is duplicated is also subjected to a <br /> spike analysis. In this technique, a third aliquot of the <br /> sample has added to it a known quantity of the analyte. <br /> The recovery on the resulting spiked sample relative to its <br /> theoretical value reflects the accuracy of the determi- <br /> nation. since percent recoveries are often strongly <br /> influenced by the sample matrix, it is more informative to <br /> spike real samples than to spike blanks. <br /> Duplicate results and spike pike recoveries are sorted by matrix <br /> type for statistical analysis and calculation of control <br /> j C charts. If a particular determination is not carried out <br /> } r frequently enough on a particular matrix t <br /> � ype for success- <br /> ful statistical manipulation, the results are grouped with <br /> others of similar matrices. <br /> s <br /> 'r <br /> V-3 <br />